The meaning of "Biscuit" in various phrases and sentences

I think my grandparents had that biscuit tin!
https://goo.gl/images/dO4ztI
"Shortbread" is a type of biscuit associated with Scotland and often sold at this time of year. That is why romantic images of Scotland might be on a biscuit tin.
Kilt, sporran and bagpipes are all part of traditional Scottish dress and music.
Probably in this case, they refer to the idea people have of Scotland, which of course is not like the everyday reality.

son of biscuit is a so called "minced" expression. it's a eufemism. It is a form of cursing without saying the bad word. It refers in this case to son of a bitch (perhaps you would use the word kisama in Japanese).

Example sentences using "Biscuit"

This colloquial phrase is used when someone has done something which you think means they are acting in an unreasonable or inconsiderate way. For example, if your colleague at work often gets other people to do his work for him and one day he asks someone to take on a lot of extra work and he is doing nothing, then you can say, “That really takes the biscuit! He should do his own work.”

For me, a cookie is a very specific type of biscuit. So if someone asked me "Do you want a cookie?" I would expect a chocolate chip cookie for example.
But a biscuit is any sort of crunchy snack/treat usually had with tea or coffee.

It’s actually very good ! And very casual sounding which is perfect. The only thing that I would maybe say a little different is “I was about to buy it, but didn’t because I already had other biscuits at home. When my family finish those, I will buy it. “
Otherwise perfect ! :)